A hybrid vehicle driveline may include a driveline disconnect clutch. The driveline disconnect clutch allows a motor in the hybrid driveline to operate independently from an engine in the hybrid driveline. During periods of low demand torque, the motor may operate while then engine is stopped and disconnected from the motor via the driveline disconnect clutch. By opening the driveline disconnect clutch, the motor may propel the hybrid vehicle more efficiently because the motor does not have to overcome engine pumping losses and engine friction. However, if the engine is stopped after operating at a higher load, a catalyst in the engine's exhaust system may reach temperatures that accelerate catalyst degradation. In particular, if the fuel supplied to the engine is cut-out and a small amount of air is allowed to flow to the catalyst before the engine has stopped rotating, hydrocarbons may combust and raise catalyst temperature higher than may be desired.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating a hybrid driveline, comprising: in response to a catalyst temperature exceeding a first threshold temperature and conditions, other than catalyst conditions, being present for opening a driveline disconnect clutch, not opening the driveline disconnect clutch.
By selectively allowing opening of a driveline disconnect clutch based on catalyst state, it may be possible to provide the technical result of reducing the possibility of catalyst degradation after catalyst temperature has been elevated. For example, if an engine has been operated at higher speeds and loads, catalyst temperature may become elevated. However, when engine load is reduced, the driveline disconnect clutch may remain engaged while lower engine exhaust temperatures cool the catalyst. Additionally, by leaving the driveline disconnect clutch closed, driveline torque disturbances may also be reduced since the driveline remains in a same operating state.
The present description may provide several advantages. In particular, the approach may reduce the possibility of catalyst degradation. Further, the approach may reduce driveline torque disturbances. Further still, the approach may reduce driveline wear, thereby increasing the operating life of the driveline.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.